1. Field of the Technology
The present invention relates to an image forming apparatus for controlling the speed of a rotation body for rotating an image carrier for performing transfer, thereby adjusting image formation, and more particularly to an image forming apparatus for measuring a transfer characteristic, thereby controlling the speed of the rotation body.
2. Description of Related Art
The image forming apparatus has a rotation body for rotating a photosensitive drum for transferring an image and an intermediate transfer belt. And, to execute precisely image formation, it is necessary to adjust accurately the rotation speed of the rotation body. To adjust accurately the rotation speed in a system requiring highly precise control for driving such a rotation body, it is desirable to confirm the transfer characteristic of the drive system and then decide a control parameter.
Further, even if it is intended to rotate independently the photosensitive drum and intermediate transfer belt, force via the intermediate transfer belt acts on the photosensitive drum and the force may affect the rotation speed of each rotation body.
Conventionally, in the image forming apparatus, the transfer characteristic is measured beforehand using a prototype and the fixed control parameter decided on the basis of the results is used. Particularly, in a control system including repeat control used when executing the control more high-precisely, since the control using an inverse characteristic (here, “inverse characteristic” means an inverse function of the function expressing the transfer characteristic) of the transfer characteristic of the drive system is utilized, when the dissociation between the control parameter and the real transfer characteristic of the apparatus is large, the controllability is lowered. Therefore, generally, within a predictable change range of the transfer characteristic of the drive system, a control parameter is set so as to make the control stability and controllability compatible with each other. However, in actual, it is difficult to expect beforehand the change range of the transfer characteristic including a change with time and variations in the components, and to widen the stable range of control results in to widen the range for permitting speed change of the rotation body and to lower the accuracy of controllability. Therefore, it is very difficult to ensure a highly precise and wide stable range of control. Therefore, an art (for example, refer to Unexamined Japanese Patent Application Publication No. H6-175427) for obtaining a transfer function of rotation control, obtain a phase margin and a gain margin from the transfer function, and when the obtained values are larger than the values indicating the stable ranges, changing the control parameter, an art (for example, refer to Unexamined Japanese Patent Application Publication No. H8-220966), even if one of the rotation members is exchanged, for newly obtaining a transfer function of the system by the speed detecting section and resetting the control parameter, and an art (for example, refer to Unexamined Japanese Patent Application Publication No. H9-182488) for storing a speed variation during one rotation of the rotation body in the steady state, deciding a dominant frequency component from the data, obtaining a frequency response of the drive transfer system, calculating a response characteristic, and executing the repeat control on the basis of the response characteristic are proposed. In these control arts, the parameter is not set beforehand using a testing machine, but the transfer characteristic is measured using a real signal in a real machine and the control parameter is changed.
Under the control aforementioned, it is possible to calculate and change the control parameter using the real signal. However, under the control aforementioned, from the control instruction value sent to the control system by the real processing and the real angular velocity detection results at that time, the transfer characteristic is obtained. In this respect, to control the rotation body, since the rotation speed of the rotation body is slow, an input value at a low frequency close to 2 or 3 Hz acts most effectively. However, when using the input value used in a real control instruction for calculation of the parameter, the low frequency component, which has a poor SN ratio, can be used hardly, thus the control parameter is calculated using the transfer characteristic for an input value at a high frequency component. Therefore, the transfer characteristic which can actually be detected is restricted, and it is difficult to obtain the necessary characteristic, and the accuracy of the control by the control parameter calculated is lowered. Furthermore, the conventional control method controls independently the intermediate transfer belt and photosensitive drum, thus it is difficult to execute control in consideration of the force affecting the rotation speed of the photosensitive drum via the intermediate transfer belt.
The present invention was developed with the foregoing in view and is intended to provide an image forming apparatus for using a test signal including from a low frequency to a high frequency, detecting a transfer characteristic based on a signal transferred to the photosensitive drum via the intermediate transfer belt, calculating a parameter for changing an inverse filter from the transfer characteristic, controlling the rotation system by the changed inverse filter, and providing an image forming apparatus which reduces the mutual effect of the rotation bodies.